A. Field of the Invention
The invention relates to separation and purification, particularly separation of crystals from a mother liquor.
B. Description of the Prior Art
Although a crystal is necessarily pure, in its preparation it will retain some mother liquor when removed from the final magma, and the adhering mother liquor will ordinarily carry impurities. If the adhering mother liquor is not removed, it will contaminate the crystal. In commercial practice, crystals are purified by centrifuging, by filtration and by recrystallization. Residual mother liquor after centrifuging is ordinarily in the range of about 2-5% or more of the weight of crystals. Large uniform crystals from low-viscosity mother liquors will retain a minimum proportion of mother liquor. Non-uniform small crystals from viscous solutions will retain a considerably larger proportion. It is common practice to wash crystals on a centrifuge or filter with a fresh solvent; and the use of counter current washing in multiple stages is known to reduce the loss of crystals by solution in the solvent. The use of a solvent requires separate steps to remove residual solvent from the product such as by drying and some means of solvent recovery. Batch press squeeze purification has been employed commercially but its lack of continuity has been a serious handicap to an otherwise continuous process.
In the commercial production of chemical compounds, particularly aromatic organic compounds, where purification is known to be a problem, any improved method of purifying would be a significant advance in the art and is an object of this invention.